Corrugated paperboard sheets produced on the dry end of a corrugator are typically shingled and then delivered to a downstacker bay where the sheets are squared in a uniform stack fed by a stacker infeed nip. The sheets exiting the nip and delivered to the stacker descend with the infeed of sheets until a stack of a desired number of sheets or height is achieved whereupon the stack is removed and the stack support is returned to a position adjacent the infeed nip.
Prior art stacker infeed nips have typically used a driven bottom roll and an idler top roll with a cushioning or zero crush cylindrical contact surface.
In stackers utilizing a single bottom drive roll for the infeed nip, “back slip” or shingle compression can occur, particularly if there are quality problems with the sheets being stacked. Back slip or shingle compression may result in the buildup of too much pressure in the nip and can result in product jam. Poor product quality may also cause a jam at the stacker infeed nip. When this occurs, cross machine direction slip of the sheets entering the stacker bay is also a problem.